The reinforcement or reinforcement armature of tires, and especially of motorcycle tires, is at the present time—and most often—formed from a stack of one or more plies conventionally denoted as “carcass plies”, “crown plies”, etc. This way of denoting the reinforcements derives from the manufacturing process, which consists in producing a series of semi-finished products in the form of plies, which are provided with often longitudinal thread-like reinforcing members that are subsequently assembled or stacked so as to build a tire blank. The plies are produced flat, with large dimensions, and are then cut up according to the dimensions of a given product. The assembly of the plies is also carried out, firstly, approximately flat. The blank thus produced then undergoes a forming operation so as to adopt the typical toroidal profile of tires. The semi-finished or “finish” products are then applied to the blank so as to obtain a product ready to be vulcanized.
Such a “conventional” process involves, in particular in respect of the phase of manufacturing the tire blank, the use of an anchoring element (generally a bead wire) used to anchor or retain the carcass reinforcement in the bead zone of the tire. Thus, for this type of process, a portion of all of the plies making up the carcass reinforcement (or only one part thereof) is turned up around a bead wire placed in the bead of the tire. This anchors the carcass reinforcement in the bead.
The generalization in industry of this type of conventional process, despite many variations in the way in which the plies and the assemblies are produced, has led those skilled in the art to use a vocabulary taken from the process: hence the generally accepted terminology comprising, in particular, the terms “plies”, “carcass”, “bead wire”, “shaping”, to denote the transition from a flat profile to a toroidal profile, etc.
Nowadays, there are tires which strictly speaking do not have “plies” or “bead wires” according to the above definitions. For example, document EP 0 582 196 discloses tires manufactured without the aid of semi-finished products in the form of plies. For example, the reinforcing elements of the various reinforcement structures are applied directly to the adjacent layers of rubber compounds, the whole assembly being applied in successive layers on a toroidal core, the shape of which results directly in a profile similar to the final profile of the tire under manufacture. Thus, in this case, there are no longer “semi-finished” products or “plies” or “bead wires”. The base products, such as rubber compounds and the reinforcing elements in the form of threads or filaments, are directly applied to the core. Since this core is toroidal in shape, it is no longer necessary to form the blank in order to go from a flat profile to a torus-shaped profile.
Moreover, the tires disclosed in the above document do not have the “conventional” carcass ply upturn around a bead wire. This type of anchoring is replaced with an arrangement in which circumferential threads are placed adjacent to said sidewall reinforcement structure, the whole assembly being embedded in an anchoring or bonding rubber compound.
There are also assembly processes on a toroidal core using semi-finished products especially suitable for rapid, effective and simple laying on a central core. Finally, it is also possible to use a hybrid comprising both certain semi-finished products, in order to produce certain architectural aspects (such as plies, bead wires, etc.), whereas others are produced by direct application of compounds and/or reinforcing elements.
In the present document, to take into account recent technological developments both in the manufacturing field and in product design, the conventional terms such as “plies”, “bead wires”, etc. are advantageously replaced with neutral terms or terms that are independent of the type of process used. Thus, the term “carcass-type reinforcing member” or “sidewall reinforcing member” is valid for denoting the reinforcing elements of a carcass ply in the conventional process, and the corresponding reinforcing elements, which are in general applied to the sidewalls, of a tire built using a process without semi-finished products. As regards the term “anchoring zone”, this may denote just as well the “conventional” carcass ply upturn around a bead wire of a conventional process as the assembly formed by the circumferential reinforcing elements, the rubber compound and the adjacent sidewall reinforcing portions of a bottom zone produced by a process with application on a toroidal core.
The longitudinal direction, or circumferential direction, of the tire is the direction corresponding to the periphery of the tire and defined by the rolling direction of the tire.
A circumferential plane or circumferential plane of section is a plane perpendicular to the rotation axis of the tire. The equatorial plane is the circumferential plane passing through the centre or crown of the tread.
The transverse or axial direction of the tire is parallel to the rotation axis of the tire.
The radial direction is a direction cutting the rotation axis of the tire and perpendicular thereto.
The rotation axis of the tire is the axis about which it rotates in normal use.
A radial or meridian plane contains the rotation axis of the tire.
As in the case of all other tires, motorcycle tires have undergone radialization, the architecture of such tires comprising a carcass reinforcement formed from one or two layers of reinforcing elements making an angle that may be between 65° and 90° with the circumferential direction, said carcass reinforcement being radially surmounted by a crown reinforcement formed from reinforcing elements. However, there are non-radial tires to which the invention also relates. The invention also relates to partially radial tires, that is to say those in which the reinforcing elements of the carcass reinforcement are radial at least over part of said carcass reinforcement, for example in the part corresponding to the crown of the tire.
Many crown reinforcement architectures have been proposed, depending on whether the tire is intended to be mounted on the front wheel of the motorcycle or on the rear wheel. A first structure consists, in the case of said crown reinforcement, in employing only circumferential cords, and said structure is more particularly employed for the rear position. A second structure, inspired directly from the structures widely used in tires for passenger vehicles, has been used to improve the wear resistance and consists in the use of at least two crown working layers of reinforcing elements which are approximately mutually parallel in each layer but crossed from one layer to the next, making acute angles with the circumferential direction, such tires being more particularly suitable for the front wheel of motorcycles. Said two crown working layers may be combined with at least one layer of circumferential elements generally obtained by the helical winding of a strip of at least one rubber-embedded reinforcing element.
The choice of tire crown architecture has a direct effect on certain properties of the tires, such as wear, endurance and grip, or else on the rolling comfort or, in particular in the case of motorcycles, on the stability. However, other parameters of the tires, such as the nature of the rubber compounds making up the tread, also have a direct impact on the properties of said tire. The choice and nature of the rubber compounds constituting the tread are for example essential parameters relating to the wear properties. The choice and nature of the rubber compounds making up the tread also have an impact on the grip properties of the tire.